A “shift drum type” transmission is often conventionally used in a straddle-type vehicle, for example. A shift drum type transmission includes a plurality of first gears provided on a main shaft, and a plurality of second gears provided on a drive shaft. The first and second gears include movable gears that are movable axially. The shift drum type transmission further includes a shift fork that axially moves the movable gears, and a shift drum provided with a groove with which the shift fork engages. The shift drum is connected to a shift shaft via a gear change mechanism. Upon rotation of the shift shaft, the shift drum rotates. Upon rotation of the shift drum, the shift fork moves along the groove. With the movement of the shift fork, the movable gears move axially. As a result, a combination of the first and second gears, which intermesh with each other and to which a torque is transmitted, is changed, thus changing a transmission gear ratio between the main shaft and the drive shaft.
The gear change mechanism includes a shift lever fixed to the shift shaft, and a rotation plate fixed to an end of the shift drum. The shift lever is arranged to be engageable with the rotation plate. Upon rotation of the shift lever with the rotation of the shift shaft, the rotation plate receives a force from the shift lever and thus rotates. The shift drum rotates with the rotation of the rotation plate. As a result, a speed change is performed.
The gear change mechanism further includes a stopper lever that holds the rotation plate at a suitable position. The stopper lever is rotatably supported by a support shaft. The stopper lever is provided with a stopper roller. An outer peripheral surface of the rotation plate is provided with a plurality of recessed portions. The stopper roller engages with the recessed portion, thus restricting rotation of the rotation plate from the suitable position and holding the rotation plate at the suitable position.
In order to restrict the rotation of the rotation plate, the stopper roller has to be pressed against the recessed portion. As a member that applies a force to press the stopper roller against the recessed portion, JP 2004-116545 A discloses a torsion spring attached to a support shaft for a stopper lever. The torsion spring is wound around the support shaft. Therefore, the torsion spring does not largely protrude around the support shaft. A gear change mechanism including such a torsion spring is advantageous in that the gear change mechanism is easily reduced in size.